Unreachable content (Docker containers) on other ports than 80

I have a problem accessing Docker containers for any other port than 80. Previously it worked and I had services accessibles on ports 5000 and 7000 in addition to a nginx server installed directly on the droplet. I recently do a dist-upgrade to Ubuntu 18.04.1 LTS and that may have broken stuff.

What works:

accessing a page on port 80 or 443 served by nginx (without docker)

accessing my docker container from another machine if bind on port 80

accessing my docker container from the localhost regardless of port

What doesn’t work:

accessing a page on port 81 served by nginx (without docker)

accessing my docker container if bind to port 5000 or 7000

So it seems there is a problem with other ports than 80 and 443 for serving content on the internet. I have no digital ocean firewall configured. I tried to look iptables stuff but I understand very little and don’t manage to find anything suspicious.